<template>
    <ul class="list">
        <li class="item"
            v-for="item of letters" 
            :key="item"
            :ref="item"
            @click="handleLetterClick"
            @touchstart.prevent="handleTouchStart"
            @touchmove="handleTouchMove"
            @touchend="handleTouchEnd"
        >
            {{item}}
        </li>
    </ul>
</template>

<script>
import { clearTimeout, setTimeout } from 'timers';
export default {
    name:'CityAlphabet',
    props:{
        cities:Object
    },
    computed:{
        letters(){
            const letters=[]
            for (let i in this.cities){
                letters.push(i)
            }
            return letters
        }
    },
    data(){
        return{
            touchStatus:false,
            startY:0,
            timer:null
        }
    },
    updated(){
        this.startY=this.$refs['A'][0].offsetTop
    },
    methods:{
        handleLetterClick(e){
            this.$emit('change',e.target.innerText)
            // console.log(e.target.innerText)
        },
        handleTouchStart(){
            this.touchStatus=true
        },
        handleTouchMove(e){
            if(this.touchStatus){
                if(this.timer){
                    clearTimeout(this.timer)
                }
                this.timer=setTimeout(()=>{
                    const touchY=e.touches[0].clientY-87.3
                    const index=Math.floor((touchY-this.startY)/20)
                    if(index >=0 && index <this.letters.length){
                        this.$emit('change',this.letters[index])
                    }
                },16)
            }
        },
        handleTouchEnd(){
            this.touchStatus=false
        }
    }
}
</script>

<style lang="stylus" scoped>
    @import '~styles/varibles.styl'
    .list
        display:flex
        flex-direction:column
        justify-content:center
        position:absolute
        top:1.74rem
        right:0
        bottom:0
        width:.4rem
        .item
            line-height:.4rem
            text-align:center
            color:$bgColor
</style>